Westlund, Anders

Abstract [en]

The work presented in this thesis is the result of the KTH CICERO project “Dynamic Engine Performance” in which the main objective was to develop simple models foremission formation. The demand for such models is increasing, mainly due to the tightening emission legislation for diesel engines which has lead to more complex engines and thereby more laborious development and calibration processes. Simple emission models can be a valuable tool during the development phase, e.g. when used with models for gas exchange - and after-treatment systems, and for precalibration of the engine control settings. Since engines in automotive application typically work under dynamic load, the main prerequisites were that the models should be comprehensive enough to handle the extreme conditions that can occur in engines during load transients but still simple enough to be used for calibration.

Two main approaches have been used; one where the combustion and emission formation processes were modeled from the flame front and downstream using equilibrium chemistry. In the other approach, the entire mixing/entrainment process was modeled and emission formation was modeled with kinetic chemistry. Both approaches were found to meet the requirements but had different advantages; the first, simpler approach had shorter calculation time while the latter was more comprehensive and required less tuning. The latter also resulted in a model for heat release rate which can be useful as a stand-alone model and allows the emission models to be used for untested conditions.

Another objective in this project was to identify techniques/instruments that can be used for emission measurements during transient operation since these are essential for understanding of emission formation in these conditions and as validation data for the emission models.

Abstract [en]

PM-emissions during a load transient have been measured regarding particle mass, exhaust transparency and particle number concentrations in different size ranges. The load transient was from low to medium load at constant speed and was performed with a single cylinder research engine. Mass measurements were conducted with a Tapered Element Oscillating Microbalance . Exhaust transparency was measured with an Opacimeter. Particle Number Concentrations were measured with two different Condensation Particle Counters , CPCs, where one of them was equipped with a Particle Size Selector , PSS, in order to distinguish accumulation mode particles from nucleation mode. An Engine Exhaust Particle Sizer , EEPS, was also used in parallel with the CPCs and provided a full size distribution. For dilution, a rotating disc diluter and a two stage ejector diluter was used. In total two stages of hot dilution and one unheated. It was found that all instruments, except the TEOM, had acceptable time resolution for dynamic measurements with the dilution and acquisition setup used in this experiment. In most aspects, the measurements from the different instruments were consistent and the discrepancies could be explained by their measuring principles. In some cases, simultaneous use of different instruments could provide a more detailed description of the emitted PM. It was also concluded that the rotating disc diluter, with some reservations, could be used for transient measurements.

Abstract [en]

A clear trend in engine development is that the engines are becoming more and more complex both regarding components and component-systems as well as controlling them. These complex engines have great potential to minimize emissions but they also have a great number of combinations of setting. Systematic testing to find these optimum settings is getting more and more challenging. A possible remedy is to roughly optimize these settings offline with predictive models and then only perform the fine tuning in the engine test bed. To be able to do so, two things are needed; firstly a engine model that will predict how the different setting affect engine performance and secondly how the engine performance affects the emissions.

Abstract [en]

A clear trend in engine development is that the engines are becoming more and more complex both regarding components and component-systems as well as controlling them. These complex engines have great potential to minimize emissions but they also have a great number of combinations of setting. Systematic testing to find these optimum settings is getting more and more challenging. A possible remedy is to roughly optimize these settings offline with predictive models and then only perform the fine tuning in the engine test bed. To be able to do so, two things are needed; firstly a engine model that will predict how the different setting affect engine performance and secondly how the engine performance affects the emissions.

Open this publication in new window or tab >>Validation of a Simplified Model for Combustion and Emission Formation in Diesel Engines Based on Correlations for Spray Penetration and Dispersion, Gas Entrainment into Sprays and Flame Lift-off

Llindström, Mikael

Abstract [en]

A simplified combustion and emission formation model for diesel engines has been developed in a project where the long term objective is to predict emissions during transient operation. The intended application implies that the final model must be both computationally inexpensive and comprehensive so that it can be used for optimization of engine control variables when coupled to full-engine simulation software. As starting point, the proposed model uses diesel spray correlations established in combustion vessels regarding spray penetration, dispersion, gas entrainment, ignition and flame lift-off. It has been found that with minor adaption, these correlations are valid also for combustion in an engine. By assuming a fully mixing controlled combustion after ignition and by use of simplified emission models, the correlations have been found useful for predicting trends in engine-out emission with low computational cost. Besides engine-out emissions and pressure analysis, endoscope instrumentation has been used to provide validation data regarding maximum in-cylinder temperature and soot concentration.

Open this publication in new window or tab >>A 1-D Model for Heat Release Rate and Emission Formation in Diesel Engines Based on Correlations for Entrainment Rate, Lift-Off Length and Ignition Delay: Validation for Transient Conditions